DECLARE @local_variable (Transact-SQL)

Variables are declared in the body of a batch or procedure with the DECLARE statement and are assigned values by using either a SET or SELECT statement. Cursor variables can be declared with this statement and used with other cursor-related statements. After declaration, all variables are initialized as NULL, unless a value is provided as part of the declaration.

Assigns a value to the variable in-line. The value can be a constant or an expression, but it must either match the variable declaration type or be implicitly convertible to that type.

@cursor_variable_name

Is the name of a cursor variable. Cursor variable names must begin with an at (@) sign and conform to the rules for identifiers.

CURSOR

Specifies that the variable is a local cursor variable.

@table_variable_name

Is the name of a variable of type table. Variable names must begin with an at (@) sign and conform to the rules for identifiers.

<table_type_definition>

Defines the table data type. The table declaration includes column definitions, names, data types, and constraints. The only constraint types allowed are PRIMARY KEY, UNIQUE, NULL, and CHECK. An alias data type cannot be used as a column scalar data type if a rule or default definition is bound to the type.

<table_type_definition> is a subset of information used to define a table in CREATE TABLE. Elements and essential definitions are included here. For more information, see CREATE TABLE (Transact-SQL).

n

Is a placeholder indicating that multiple variables can be specified and assigned values. When declaring table variables, the table variable must be the only variable being declared in the DECLARE statement.

column_name

Is the name of the column in the table.

scalar_data_type

Specifies that the column is a scalar data type.

computed_column_expression

Is an expression defining the value of a computed column. It is computed from an expression using other columns in the same table. For example, a computed column can have the definition cost AS price * qty. The expression can be a noncomputed column name, constant, built-in function, variable, or any combination of these connected by one or more operators. The expression cannot be a subquery or a user-defined function. The expression cannot reference a CLR user-defined type.

[ COLLATE collation_name]

Specifies the collation for the column. collation_name can be either a Windows collation name or an SQL collation name, and is applicable only for columns of the char, varchar, text, nchar, nvarchar, and ntext data types. If not specified, the column is assigned either the collation of the user-defined data type (if the column is of a user-defined data type) or the collation of the current database.

Specifies the value provided for the column when a value is not explicitly supplied during an insert. DEFAULT definitions can be applied to any columns except those defined as timestamp or those with the IDENTITY property. DEFAULT definitions are removed when the table is dropped. Only a constant value, such as a character string; a system function, such as a SYSTEM_USER(); or NULL can be used as a default. To maintain compatibility with earlier versions of SQL Server, a constraint name can be assigned to a DEFAULT.

constant_expression

Is a constant, NULL, or a system function used as the default value for the column.

IDENTITY

Indicates that the new column is an identity column. When a new row is added to the table, SQL Server provides a unique incremental value for the column. Identity columns are commonly used in conjunction with PRIMARY KEY constraints to serve as the unique row identifier for the table. The IDENTITY property can be assigned to tinyint, smallint, int, decimal(p,0), or numeric(p,0) columns. Only one identity column can be created per table. Bound defaults and DEFAULT constraints cannot be used with an identity column. You must specify both the seed and increment, or neither. If neither is specified, the default is (1,1).

seed

Is the value used for the very first row loaded into the table.

increment

Is the incremental value added to the identity value of the previous row that was loaded.

ROWGUIDCOL

Indicates that the new column is a row global unique identifier column. Only one uniqueidentifier column per table can be designated as the ROWGUIDCOL column. The ROWGUIDCOL property can be assigned only to a uniqueidentifier column.

NULL | NOT NULL

Are keywords that determine whether null values are allowed in the column.

PRIMARY KEY

Is a constraint that enforces entity integrity for a given column or columns through a unique index. Only one PRIMARY KEY constraint can be created per table.

UNIQUE

Is a constraint that provides entity integrity for a given column or columns through a unique index. A table can have multiple UNIQUE constraints.

CHECK

Is a constraint that enforces domain integrity by limiting the possible values that can be entered into a column or columns.

Variables are often used in a batch or procedure as counters for WHILE, LOOP, or for an IF...ELSE block.

Variables can be used only in expressions, not in place of object names or keywords. To construct dynamic SQL statements, use EXECUTE.

The scope of a local variable is the batch in which it is declared.

A cursor variable that currently has a cursor assigned to it can be referenced as a source in a:

CLOSE statement.

DEALLOCATE statement.

FETCH statement.

OPEN statement.

Positioned DELETE or UPDATE statement.

SET CURSOR variable statement (on the right side).

In all of these statements, SQL Server raises an error if a referenced cursor variable exists but does not have a cursor currently allocated to it. If a referenced cursor variable does not exist, SQL Server raises the same error raised for an undeclared variable of another type.

C. Declaring a variable of type table

The following example creates a table variable that stores the values specified in the OUTPUT clause of the UPDATE statement. Two SELECT statements follow that return the values in @MyTableVar and the results of the update operation in the Employee table. Note that the results in the INSERTED.ModifiedDate column differ from the values in the ModifiedDate column in the Employee table. This is because the AFTER UPDATE trigger, which updates the value of ModifiedDate to the current date, is defined on the Employee table. However, the columns returned from OUTPUT reflect the data before triggers are fired. For more information, see OUTPUT Clause (Transact-SQL).

D. Declaring a variable of user-defined table type

The following example creates a table-valued parameter or table variable called @LocationTVP. This requires a corresponding user-defined table type called LocationTableType. For more information about how to create a user-defined table type, see CREATE TYPE (Transact-SQL). For more information about table-valued parameters, see Table-Valued Parameters (Database Engine).